1. Field of the Invention
The present invention relates to an optical position detecting unit, an optical coordinate input unit and an optical position detecting method. Particularly, it relates to an optical position detecting unit including an optical position pointer and a single photodetector. The position pointer includes a light-emitting portion for pointing its existing position by light emitted from the light-emitting portion and the photodetector detects the light. The optical position detecting unit detects the coordinates of a position pointed by the optical position pointer on the basis of the distance to the light-emitting portion and the direction of incidence of the light, both of which are detected by the single photodetector. Further it relates an optical coordinate input unit configured by using the optical position detecting unit, and an optical position detecting method of measuring the distance to the light-emitting portion by using the single photodetector.
2. Description of the Related Art
Heretofore, PSD (Position Sensitive Light Detector) is well known as an example of the unit for detecting position, direction, etc. The PSD is a light sensor by which the position of a spotlight radiated onto its light-receiving surface can be detected as a position on the light-receiving surface. The PSD in combination with a freely movable point light source can produce a position detecting unit for detecting the position of the existence of the point light source, or a direction detecting unit for detecting the direction of incidence of light from the point light source, or a distance measuring unit for measuring the distance between the point light source and a body of the detector, as described in "Production of Distance Detector using PSD", pp. 79-88, August 1990 issue of Transistor Technique.
JP-A-5-19954 discloses a conventional unit for obtaining indicated position information by using an optical configuration. This conventional unit includes a movable body with a light-emitting element which is moved on an operation table defining an XY coordinate plane thereon, and an X light-receiving portion and a Y light-receiving portion arranged respectively in the center of an X-direction side and a Y-direction side in the operation table. The conventional unit is configured such that light from the light-emitting element of the movable body is converged by an optical lens included in the respective light-receiving portions to thereby form images, and such that the X and Y coordinate values of the position designated by the movable body are obtained by using information of image-formed positions in the respective light-receiving portions.
In order to detect the position of a point light source by using the PSD, light coming from the point light source must be focused into a spotlight before the light is radiated onto the light-receiving surface for detection. To this end, it is necessary to provide an optical lens excellent in converging performance. Since the PSD is limited in the detectable distance between the light-receiving surface and the point light source, there is a significant limit in its practical use. Further, in the PSD, correction processing is required in order to obtain required detection accuracy. Also, in the optical coordinate information output unit disclosed in the literature (JP-A-5-19954), light from the light-emitting element must be converged onto the light-receiving portions through the optical lens so as to form spotlight-shape images on the light-receiving portions in order to obtain information of the position designated by the movable body. Accordingly, like the PSD, optical lenses excellent in converging performance are required from the point of view of detection accuracy.